Optimize js-jsx--matching-close-tag-pos

Optimize js-jsx--matching-close-tag-pos

This function’s performance was having a noticeable impact when
editing large JSX structures.  Improve its performance
slightly (elapsed time will be cut in half according to ELP).

* lisp/progmodes/js.el (js-jsx--tag-re): Remove.
(js-jsx--matched-tag-type): Simplify implementation with respect to
the new implementation of js-jsx--matching-close-tag-pos.
(js-jsx--self-closing-re): Simplify regexp slightly in sync with a
generally simpler matching algorithm.
(js-jsx--matching-close-tag-pos): Optimize matching algorithm by using
multiple simple regexp searches, rather than one big complex search.

* test/manual/indent/jsx-unclosed-2.jsx: Use the term “inequality” and
add a test for a possible parsing foible.